Variable vanadium

Materials World magazine

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8 Oct 2010

Michael Forrest reports on the increasing popularity of this ductile transition metal.

The debate over the efficiency of wind farms and their need for back-up generation will continue as long as there is no effective way to store the electrical energy they generate. The same can be said for solar-generated power. One answer is the use of vanadium redox batteries that can withstand rapid charge and discharge almost indefinitely and are scalable to any size. In portable lithium batteries, vanadium is a component that can provide a higher output in kWh/Kg than cobalt, manganese, iron or phosphorus additions, although at a higher price.

Although these new uses for vanadium have excited the market, over 85% of the global production of 54,000t of contained vanadium (USGS Data) is used in steel, the bellwether of the global economy. Mine supply accounts for approximately 40%, with the remainder coming from the processing of slags, mainly from magnetite ores used in making steel, with a small amount from oil residues and ashes from refineries and power stations.

This dominance of by-product leads to under and over production relative to the vanadium market, and consequently its price has fluctuated widely in the past. For example, prices in the past 36 months have varied from <US$5/lb to >US$17/lb in the international market. Furthermore, mine and slag production is dominated by just three countries – China, Russia and South Africa, adding a degree of political uncertainty to supply, particularly apparent in the USA, which imports 100% of its needs.

Fluctuating value

One company that sees these problems as opportunities is Rocky Mountain Resources and its CEO Bill Radvak, a mining and mineral processing engineer. He says, ‘The burgeoning use of vanadium in hi-tech applications, such as aerospace alloys and in battery technology, demands security of supply at a steady price, facilitating future investment and planning. That, in turn, requires primary production that is not by-product dependent’. Vanadium is at relatively low concentrations in the earth’s crust and even in mineralised formations rarely exceeds 0.5%. In slags, vanadium values can vary from less than 0.01% to several per cent, according to the ore used, and, as a result, processing of vanadium-bearing ores must be efficient to compete with recovery from slags.

‘This presents a challenge to any new vanadium project’ declares Radvak. A way must be found that is robust in economic terms and can survive the variable vanadium price as steel demand fluctuates. That, in turn, requires a deposit with favourable geological and metallurgical parameters. ‘We believe we have such a deposit. It is located some 40km south of Eureka in Nevada, USA – a state with mining-friendly regulation, strong infrastructure and a well-established mining industry that can supply everything from equipment to skilled workers. We cannot claim to have discovered the deposit, nor can we claim to be the first to examine its potential for vanadium production. However, we have a proven recovery process that will firmly establish the project as one with the lowest costs – a necessary prerequisite to enter the vanadium market.’

The work of a number of companies, including Union Carbide and Noranda, over the years has been useful in determining the resources at Gibellini, an area of 3,400 acres of claims held by Rocky Mountain. The original discovery, in 1942, by Louis Gibellini was of nickel and manganese, mined intermittently into the 1950s.

In 1956, Union Carbide discovered vanadium mineralisation one mile to the south and began determining resources through drilling. Four other companies conducted later drilling campaigns using mainly rotary and reverse circulation. Overall, 25,000ft of rotary and 10,700ft of reverse circulation were drilled, but unfortunately no cuttings or cores remain. ‘Although good drill logs were kept, describing lithologies and mineralisation, we needed a better definition of resources,’ says Radvak. Rocky Mountain contracted AMEC plc to review the existing data including logs and analyses. Their conclusion was that the logs were well executed and there was insignificant down-hole contamination.

In the zone

The vanadium mineralisation is in a regional setting, typical of basin and range geology of the western USA. Locally, the deposit is hosted in an allochtonous (formed elsewhere) wedge of organic-rich mudstone, silt and chert, forming a prominent northwest-trending ridge where outcrops are scarce except for along road cuts and trenches. The black shale unit, which hosts the vanadium resource, is from 175ft to over 300ft thick and overlies gray mudstone. The shale has been oxidised to various hues of yellow and orange up to a depth of 100ft. The overthrust eastward occurred during the Antler Orogeny in late Devonian time.

The AMEC review gave a number of useful suggestions for future work states Radvak, including revising a leaching test. One of their conclusions was that the vanadium was held as an oxide and that the degree of grinding made little difference to the recovery. This supports previous work that maintained that the vanadium was held as coatings on the rock fragments. In addition, bottle roll tests, using the equivalent of 300kg of sulphuric to one tonne of ore, suggested that less acid would achieve a similar recovery. These factors led Radvak to believe that the ores may be suitable for heap leaching with economic acid use and vanadium recovery. ‘This will be a first, as no other plant at this time is using heap leaching for the recovery of vanadium. Heap leaching is an extremely low cost activity, and we have devised a flow sheet for processing the ore that gives acceptable recoveries.’

‘We are currently working on the scoping study proposed by AMEC and upgrading the processing route to prepare a feasibility study. Using a 0.1% cut-off grade, the revised indicated resource of 18Mt at 0.34% gives a contained 122Mlb with a low strip ratio of 0.2 (waste1: ore 5). Inferred resources are 16Mlbs at a grade of 0.28%,’ notes Radvak. Metallurgical research has revealed that curing (pretreating) with sulphuric acid before leaching increases recovery and reduces overall acid consumption. Adding 10% extra water also helps and gives recovery rates between 70-90% from different samples.

Looking to the future, the base case is to mine around 2,000t per year over a nine-year mine life, with an annual production of 14Mlbs of vanadium pentoxide at an operating cost of US$3.0/lb. Capital costs are estimated at US$94m, a fraction of the cost of a pyro-metallurgical plant. ‘This is a manageable cost for a junior company. We expect the feasibility study to be completed mid 2011 and in production by the end of 2012.

‘The market for vanadium has been growing at six per cent per annum over the past decade, about double that of carbon steel as the strength advantages imparted by vanadium are recognised. The dependence on by-product has curtailed investment in the past, but we believe that the low cost breakthrough in heap leaching will allow profitable mine production’, adds Radvak.